Hello, I'm Dr. Deb and will do my best to help you.
I'm so sorry that you dog has cut his tongue; I've had this happen to one of my own dogs and I know how much blood can be produced!
The answer to your question depends on the severity of the wound and if you can visualize it (which isn't always easy when the tongue is involved). If it's deep, then it may need to be sutured; however, if it's a small cut, then the bleeding will eventually stop on its own although it might take several hours for it to do so.
The problem is that direct pressure usually can't be applied to the tongue and every time the patient licks their lips or moves their tongue, the bleeding will start fresh again. It's difficult for a clot to form and remain in place when this happens.
If there's only drops of blood being produced, then he should be fine but if it's gushing quite a bit, then it may be prudent to have him seen.
Trying to keep him quiet so that his blood pressure isn't high can help to slow things down as well. And, keeping him cool so he doesn't pant may be helpful as well.
I hope this helps. Deb